This invention relates generally to interface or conversion circuits and more particularly, it relates to a BICMOS (bipolar/CMOS mixed type) ECL-to-CMOS conversion circuit having high current drive capability and low propagation delay for receiving ECL input level signals and for producing output signals which are CMOS compatible.
CMOS or TTL logic levels have larger voltage swings (CMOS level has a voltage swing of approximately 5.0 volts and TTL level has a voltage swing of approximately 3.0 volts) so that they are easier to meet the required levels. This means that CMOS or TTL logic circuits can be fabricated at lower cost. However, they become inherently slow and noisy due to the fact of the higher voltage swings. On the other hand, ECL logic levels has a smaller voltage swing (about 0.8 volts) so that it is more difficult to meet the required levels. It normally requires good bipolar transistors to achieve the required levels. As a result, this increases manufacturing costs. Also, ECL logic inherently controls signals by switching constant currents so that it has high power consumption to maintain the high speed. Of course, ECL logic provides higher speed without making noise by running high currents.
Therefore, it would be desirable to place both ECL and CMOS/TTL levels in a single semiconductor chip or single system in order to gain better performance with lower cost. For example, memories using BICMOS technology commonly use CMOS level for memory core, decoders and control logic units to obtain higher density, higher yield, higher soft-error immunity, and lower power consumption. In contrast, ECL level is used for input and output circuits to achieve higher speed with lower noise for inter-chip interface. Thus, translation circuits to convert data between ECL levels and CMOS or TTL levels become desirable.
Traditionally, MOS translators are slow just as are common MOS circuits. On the other hand, bipolar translators suffer from the disadvantage of high power consumption in order to obtain high speed and they often require PNP-type bipolar transistors and/or Schottky diodes which further complicate the processes in fabricating the translators. Therefore, it would be highly desirable to merge or combine the CMOS and bipolar technologies together so as to make a BICMOS translator which has all of the advantages of the CMOS and bipolar technologies but yet have none of their disadvantages.